Temperature regulator for a substrate in vapor deposition processes

ABSTRACT

A heat transfer regulating mixture having a metallic component A with a melting point T A  and a particulate ceramic component B which is non-wettable by the metallic component A, non-reactive therewith and which has a melting temperature T B  which is higher than both the temperature T A  and a desired operating temperature T D  which is also higher than T A . The metallic component A and the particulate ceramic component B and the respective amounts will typically be selected to have a higher thermal resistivity above T A  than below T A . The heat transfer regulating mixture may be incorporated in the heat transfer regulating device having the mixture within an enclosure having first and second contact faces.

This application claims benefit of United States Provisional ApplicationNo.: 60/167,696, filed Nov. 19, 1999.

FIELD OF INVENTION

This invention is related to regulating the temperature of a substrateutilized in vapour deposition, in particular, in chemical vapourdeposition.

BACKGROUND OF THE INVENTION

Chemical and physical vapour deposition processes developed in the lastfew decades can produce high purity substances in commercial quantities.One of the more significant of such processes is, for example, theproduction of diamonds, usually in the polycrystalline state, utilizinga plasma source. The production of diamonds by vapour deposition isaccompanied by high thermal energy transfer. Should the heat transferand substrate temperature regulation be inadequate, the crystallizationand rate of growth of the deposit obtained, in particular, the uniformquality of the deposited diamond cannot be maintained. In other words,the temperature regulation and control of the substrate is a criticalfeature in both a physical or a chemical vapour deposition (CVD)process. A frequently implemented method of substrate temperaturecontrol is regulating the heat loss of the substrate support orsubstrate mount means. Regulated heat loss of the substrate support orsubstrate mount is usually effected by conducting heat away in acontrolled manner by some medium in contact with the substrate mount, aswell as by regulating the heat removed by a heat sink. In U.S. Pat. No.5,527,392, issued to Snail et al. on Jun. 28, 1996, a device forcontrolling the temperature of the substrate mount in a CVD reactor isdescribed. A mixture of gases having such composition as to yield adesired mean thermal conductivity, is fed to the device, to flow atknown flow rates about and around the substrate mount located in ahousing. In addition, the geometry and the material of which thesubstrate mount is made of, are selected to provide further control ofthe heat transfer capability of the substrate mount. The housing acts asthe heat sink, and has means for a cooling fluid as well. One of thedifficulties with the above arrangement is that large and cumbersome gastanks need to be installed to provide steady and reliable gas flows, asthe heat control system is very sensitive to changes in the gascomposition.

The metallurgical industries have been using sand or similar inertparticles and air circulating between the particles in a vat or in apile, for surrounding a large metal body which has been previouslyheated to a very high temperature, or for encasing a casting, to providea particulate medium for controlled or slow cooling of the metal body orcast. There are known heat transfer methods utilizing multi-phasesystems in other industries. For example, U.S. Pat. NO. 5,170,930,issued to T. P. Dolbear et al. on Dec. 15, 1992, describes a liquidmetal paste for utilization in fast cooling of electronic components andsolid state chips. The semi-solid paste is made up of low melting metalsand alloys, and solid particles of higher melting point materials, or insome instances, ceramic particles. The paste is required to have highviscosity, be both electrically and thermally conductive at temperaturesclose to room temperature, and have additional characteristics specifieduseful in the electronics industry. It is noted that the primaryfunction of the metal paste is to conduct heat away fast, and not toregulate the temperature of the electronic component at a certain level.Another multi-phase composition for fast cooling is described in U.S.Pat. NO. 5,604,037, issued to J. -M. Ting et al. on Feb. 18, 1997. Themulti-phase composition comprises a diamond/carbon/carbon fibrecomposite coated with a metallic layer for use as a dielectric heat sinkin electronic systems.

In the above multi-phased cooling devices utilized by the electronicsand metallurgical industries heat is removed, but no importance isattached to maintaining the temperature of the system underconsideration at a prerequisite level. There is a need for regulatingthe temperature of a substrate or the surface temperature of a substrateengaged in an exothermic reaction yielding a deposit, by regulating theheat loss by means of controlled heat transfer.

SUMMARY OF THE INVENTION

A heat transfer regulating mixture having a metallic component A with amelting point T_(A) and a particulate ceramic component B which isnon-wettable by the metallic component A, non-reactive therewith andwhich has a melting temperature T_(B) which is higher than both thetemperature T_(A) and a desired operating temperature T_(D) which isalso higher than T_(A) . The metallic component A and the particulateceramic component B and the respective amounts will typically beselected to have a lower thermal resistivity above T_(A) than belowT_(A) .

The metallic component A may be aluminum, tin, lead, gallium, indium,copper, silver and alloys thereof.

The particulate ceramic component B may be of alumina, titanium nitride,titanium carbide, titanium carbonitride, boron nitride, boron carbide,silicon carbide, silica and mixtures thereof.

The particulate component B may have an average particle size from 1 μmto 150 μm.

The heat transfer regulating mixture may be incorporated in the heattransfer regulating device having the mixture within an enclosure havingfirst and second contact faces.

The heat transfer regulating device may be a cooking vessel, a shieldwall, tube furnace or part of a substrate holder assembly for supportinga substrate body during a vapour deposition process.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are:

FIG. 1a is a graphical representation of the influence of the meltingpoint of a lower melting component A on the heat transferred from thesubstrate;

FIG. 1b shows the mean temperature of the substrate oscillating betweena depositing temperature and the melting point of the lower meltingcomponent A;

FIG. 2 is a schematic representation of a substrate holder assemblyaccording to the present invention, including the heat transferregulating composite mixture, and a multi-staged heat sink;

FIGS. 3a and 3 b are horizontal and cross-sectional views, respectively,illustrating a single substrate holder arrangement according to thepresent invention;

FIG. 4a and FIG. 4b are horizontal and cross-sectional views,respectively, of a multi-substrate holder arrangement according to thepresent invention;

FIG. 5 is a graph illustrating the effect of the composition of atwo-phase mixture of the present invention, on the temperature of asubstrate used in a vapour deposition process;

FIG. 6 is a schematic representation of fry pan with bottom cavityfilled with thermal regulating composite mixture according to thepresent invention;

FIG. 7a is a sectional view through a tube furnace incorporating a heattransfer regulating mixture according to the present invention;

FIG. 7b is an axial sectional view of an alternate embodiment of a tubefurnace incorporating a heat transfer regulating mixture according tothe present invention;

FIG. 8 is a graph illustrating temperature versus time characteristicsof a tube furnace according to FIG. 7a or 7 b;

FIG. 9 is a schematic illustration of a thermally resistant shield plateaccording to the present invention for use as a thermal barrier shieldagainst impact with high temperature atmospheric flow at supersonicvelocities;

FIG. 10 is a schematic illustration similar to FIG. 9, but showing asubstrate to be coated and placed near a stagnation point of hightemperature supersonic plasma flow; and,

FIG. 11 is an axial sectional schematic representation illustrating theuse of a thermal regulating compound according to the present inventionas a thermal regulating and support medium in a sliding bearingarrangement for supporting rotating parts exposed in a thermal transferenvironment.

The preferred embodiments of the invention illustrated by examples willbe described below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The formation of a vapour deposited layer of a substance on a substrateis usually accompanied by the generation of substantial amounts of heat.The generated heat needs to be removed, preferably at a controlled rate.If the heat generated is not removed in a controlled and regulatedmanner the vapour deposited layer can exhibit irregular morphology,internal stresses and uneven thickness, the substrate may developcracks, or/and irregularities of similar nature may be encountered. Onemethod of having a controlled heat transfer is to encase or surround thesubstrate, including a substrate mount, in a medium which has a heattransfer coefficient λ, selected for the specific conditions of thevapour deposition process. In the instance of a multi-component systemproviding a heat energy removal means, the heat transfer coefficient λcan be computed as a mean value of the heat transfer coefficient of eachcomponent. It is to be noted, however, that the mean heat transfercoefficient derived for a specific set of conditions of a vapourdeposition process, cannot adapt itself to unforeseen and unexpectedchanges in the variables of the deposition process, or in other words,it does not usually provide automatic regulation of the temperature ofthe substrate.

For the sake of clarity, definition of what is understood by some of theterminology used in the discussion of the preferred embodiment of thepresent invention is provided below.

“Substrate” is understood to mean a three dimensional body providing thesurface on which the vapour species is deposited. Usually but notnecessarily, only a portion of the surface, most frequently the surfacein the proximity of one end of the substrate body, is utilized as thedepositing surface, and the other end of the body of the substrate isattached to or is supported by, a substrate mount or holder. It ispreferred that the depositing surface of the substrate has close touniform temperature, while the rest of the substrate body is in atemperature gradient.

“Plasma” is considered to mean an atmosphere of low pressure and hightemperature, containing ionized gaseous species. Not all the gases inthe plasma are ionized, but it is usual that the species to be depositedis ionized. The components of a plasma often include argon or similarinert gases, both in the atomic state and in an ionized state. Othergases which may be utilized in a plasma are nitrogen, methane, oxygen,water, vaporized metal, short chained hydrocarbons, and similar gaseswhich can take part in forming an element or a compound which is to bedeposited. The plasma utilized in diamond or diamond-like coatingdeposition usually contains ionized methane gas.

“Heat sink” is commonly understood to mean a body or a series of bodieswhich remove heat predominantly by means of heat conduction or heatenergy flow. A heat sink may be composed of several stages, eachrepresenting a certain thermal resistance manifested by a temperaturegradient. A typical example of a heat sink stage is a metal body havingwater at ambient temperature circulated therethrough, in contact withanother body at a higher temperature.

It has now been found that if a two-phase mixture is provided composedof a relatively low melting alloy or metal and a particulate ceramicmaterial which conducts heat relatively well, an auto-regulating heattransfer system can be obtained. To obtain a satisfactoryauto-regulating heat transfer system the metal or alloy should have amelting point preferably 200-800° C. below the desired temperature ofthe depositing surface of the substrate, that is the temperature of thevapour deposition process, T_(D) . For obvious reasons, the meltingtemperature of the particulate ceramic material is usually substantiallyin excess of the temperature of the substrate. The selection of theceramic material as a component of the two-phase mixture is governed bythe process parameters. In other words, the melting point of metal oralloy forming the two-phase mixture in contact with the substrate islower than the temperature at which the deposit is obtained, which isconsiderably lower than the melting temperature of the particulateceramic. In general terms, if the mixture is made up of component A andcomponent B, having melting temperatures T_(A) and T_(B), respectively,then for best results, the relationship T_(A)<T_(D)<T_(B) has to hold.It is, however preferred, that the molten component A does not wet theparticulate component B.

In the instance of depositing a microcrystalline layer of diamonds on aparticular substrate the selected substrate depositing temperature T_(D)is around 900° C. The substrate is in contact or is encased, except forthe depositing surface, by a mixture of a metal or alloy having meltingpoint between 200° C. and 700° C., and ceramic particles, such asalumina, TiN, SiO₂ in the form of sand or quartz, or a mixture of thesesubstances. Other ceramic particles which may be suitable as a componentof the two-phase mixture of the present invention include boron nitride,boron carbide, silicon carbide, titanium carbide, high meltingcarbonitrides and oxynitrides, or chemical equivalents, and mixtures ofsuch. The metal-ceramic particle mixture provides a semi-solid paste, ora highly viscous liquid bearing suspended solid particles, when incontact with the substrate at the temperature of the vapour depositionprocess, such as deposition of diamonds. When the heat is removed toofast, or the substrate temperature drops below the desired temperature,the two-component mixture freezes or solidifies, leading to poor oruneven contact between the mixture and the substrate. The effect on theheat removed, of the melting temperature of the lower melting componentin the two-phase mixture in the neighbourhood of its melting point, isshown schematically in FIG. 1a, where R_(TC) is the thermal contactresistance of the two component mixture, expressed as cm²·° C./watt, andT_(A) is the melting point of the lower melting component, usually ametal. It can be seen that the thermal resistance has a low value whenthe mixture in thermal contact with the substrate, is composed of aliquid metal and a suspension of ceramic particles, resulting in highheat flux. The high heat flux lowers the temperature of the substrate incontact with the mixture, leading to the freezing of the mixture, thussevering contact between the mixture and the substrate, therebyincreasing the thermal resistance and lowering the value of heat flux,or the rate of heat transfer per unit area. Lower heat flux or lowerrate of heat transfer from the substrate results in an increase in thesubstrate temperature, which in turn, leads to the remelting of thetwo-component mixture and to the restoration of heat removal rate to theprevious level. Thus the heat flux from the substrate, and hence thesubstrate temperature (T_(st)) will oscillate around an average valueT_(P), between the depositing temperature T_(D) and the melting pointT_(A), of the metallic component of the two-phase mixture, as shownschematically in FIG. 1b, and can be described by the inequalityT_(A)<T_(P)<T_(D).

In the preferred embodiment of the invention, the substrate has aportion of its surface pre-treated to be able to receive the vapourdeposited species. The pre-treatment usually includes mechanical andconventional cleaning process steps, and other known treatments torender the substrate surface receptive of the deposited species. Thesubstrate is usually mounted in a substrate holder or mount, supportedon a base or housing, which is immersed in an atmosphere containing thevapour to be deposited. As discussed above, the substrate is encased oris surrounded below the pre-treated portion of the surface, by aphysical mixture of a low melting point metal or alloy and small sizedparticles of a ceramic material. The base supporting the substrate isusually made of metal, which represents the first stage of aconventional heat sink. Depending on the dimensions and on the nature ofthe base, the first stage of the heat sink has a certain thermalresistance, R₁. In the most simple case, the heat sink has only onestage, providing heat transfer between the substrate, the temperature ofwhich is close to the melting temperature T_(A) of the lower meltingcomponent of the two-phase mixture, and the exit temperature T_(L) ofthe cooling liquid or fluid, circulating in the housing supportingsubstrate base. Thus R₁˜(T_(A)−T_(L))/Q, where Q is the heat fluxmeasured in watts per cm², (w.cm⁻²), and R₁ has dimensions cm²·° C./w.For example, when Q=100 w·cm⁻², and (T_(A)−T_(L)) is 500° C., the valueof the thermal resistance R₁ is close to−5cm²·° C./w.

In more complex designs, the substrate base and the housingincorporating the base, may be supported on another metal blockincorporating circulating oil or a similar cooling fluid, thus providingthe second stage of a conventional heat sink arrangement, having asecond thermal resistance, R₂. The last stage of the heat sink isfrequently, however, not necessarily, another conventional water cooledmetal structure, providing yet another thermal resistance R₃. Thus theheat sink channels the heat transferred through several stages ofthermal resistance to the ambient temperature in a conventional manner.A schematic representation of the preferred embodiment of the presentinvention is shown on FIG. 2. An assembly 10, utilized in avapourdeposition process contains an elongated substrate body 14, having adepositing surface 12, which is immersed in a high temperatureatmosphere 26, containing the species to be deposited. A stem 18, of thesubstrate 14 is held in a substrate mount or substrate holder 20, whichis in contact with or is supported on a substrate mount base 22. Thesupporting base 22, and the substrate mount 20, may constitute a singleentity or may be separate units. The assembly has a water cooled base24, in direct contact with ambient temperature. The substrate stem 18 issurrounded by a composite two-phase mixture 16, composed of a lowmelting metal A, of melting point T_(A), and a particulate ceramicmaterial B, non-wetted by A, having melting point T_(B) well in excessof the depositing temperature T_(D). In the instance of diamonddeposition, the atmosphere in which the substrate is immersed, is aplasma bearing ionised carbon. A convenient plasma composition fordiamond deposition is a mixture of methane gas, hydrogen and an inertgas, such as argon. When the vapour deposited layer attains a desiredthickness the substrate is removed from the vapour bearing atmosphere,or in this particular process, from the ionised carbon containingplasma, and a fresh substrate is placed in the depositing chamber.

The metal in the two-component mixture can be tin, lead, aluminum,indium, gallium, copper-silver alloy, and an alloy of these metals, orany other similar low melting metal or alloy which is not affected bythe surrounding atmosphere. The particle size of the metal beforemelting is not critical, but to ensure good mixing the particle size ofthe metal powder is preferably between 1 and 10 μm. As has beenmentioned above, the particulate ceramic may be one or a mixture ofalumina, silica, titanium nitride, titanium carbide, titaniumcarbonitride, boron carbide, boron nitride or materials which have highmelting temperature, are oxidation resistant, are also relatively goodheat conductors and are not wetted by the metal in combination with theyare used. The average particle size is dictated by convenience and isusually less than 1 μm.

The composition and the ratio of the low melting metal or alloycomponent to the ceramic component in the two-phase mixture isdetermined by the nature of the deposited coating, the desired coatingthickness, the ultimate purpose of the vapour deposition process, thesize of the substrate, the temperature of the vapour depositing reactionand similar process considerations. The convenient ratio in weight, ofthe low melting metal or alloy to the ceramic particles ranges between10:90 and 80:20.

The pre-treatment of the depositing surface of the substrate can includeusual process steps such as grinding, polishing, cleaning, preheating,etching, ion cleaning, ion nitrating, coating with a non-reactive layer,priming of the surface and treatment by radiation.

A single substrate holder assembly and its cross-section at thesubstrate stem level is illustrated in FIGS. 3a and 3 b. The substratecarrying assembly 30, has a substrate holder base 32, a housing 34, asubstrate holder O-ring 35, a substrate mount 36, which is designed tohold a substrate 40, and a two-phase composite mixture 38 of the presentinvention. The substrate 40, having a depositing surface 42, is held incontact with the two-phase mixture 38, within the mount 36. A substratemount support 55, is a metal tubing which supports substrate mount 36,and also serves as a means to transfer heat energy to the various heatsink stages. The cross-section of the substrate mount 36 is shown inFIG. 3b, where like items are indicated by like reference numerals.

A multi-substrate holder 50 is shown in FIG. 4a, and its cross-sectionalview in FIG. 4b. The multi-substrate holder assembly 50, has componentssimilar to the single substrate holder assembly 30, of FIG. 3a,indicated by reference numerals 32, 34, 35, 36, and 55. The two-phasemixture 38 in this case is in contact with a plurality of substratestems 44, arranged in a circle around a mount seal 46. A cross-sectionalview of the substrate mount 36, having substrate stems 44 in a circularformation, packed with the two-phase mixture 38, and held in position bythe mount seal 46, is shown in FIG. 4b.

The plasma creating gas in the vapour depositing processes utilizing thetwo phase composite mixtures for regulating the temperature of thevapour deposition may include one or more of nitrogen, methane andsimilar short chained hydrocarbon, oxygen, hydrogen, water, inert gases,and vaporized metal.

EXAMPLE 1

Metal rods of 2 mm diameter, made of tungsten alloyed with 2 wt %lanthanum, were cut into 19 mm lengths, to be made into dental drills bycoating each 19 mm rod with a layer of vapour deposited polycrystallinediamond. The metal drill substrates to be coated were first mechanicallypolished by sandblasting with silicon carbide of 100 μm size, cleanedultrasonically in an acetone bath, and then the surface to be coated wasprimed by dipping into a isopropyl alcohol suspension of submicron sizeddiamonds to provide seeding.

Composite mixtures were made of fine tin of particle size 1-5μm andboron nitride having particle size less than 1 μm. The tin content ofthe composite mixtures were as follows: 20%, 40% and 80%, and anadditional test with no tin added.

Twelve (12) pretreated drill substrates for vapour deposition wereplaced in a multi-substrate holder 36, as shown in FIG. 4, packed withone of the above tin-boron nitride composite mixtures for controllingand regulating thermal energy transfer, and the drills surrounded by thecomposite mixture were held in position by the mount seal 46. Thesubstrate holder with 12 drills, was subsequently placed in an arcassisted CVD reactor, such as for example, described in U.S. Pat. No.5,587,207, to be coated with vapour deposited, polycrystalline diamondcoating. The gas in the reactor was composed of argon, hydrogen andmethane in a ratio: Ar:H₂:CH₄=2000:500:4. The temperature of thesubstrate holder during vapour deposition was measured by means of aprecision thermocouple brazed to one of the drills held in the substrateholder. The power flux proceeding from the arc plasma column towards thesubstrate surfaces was 10 watt.cm⁻². The duration of each diamondcoating deposition utilizing two phase composite mixtures of differenttin content was 12 hours.

The temperature of the substrate holder during the vapour depositionprocess was plotted against the tin content of the two phase mixturesurrounding the drills, starting with pure boron nitride powder. Theresults are shown on FIG. 5. It is noted, that in the absence of tin inthe thermal energy transfer regulating substance high but rapidlyfluctuating temperatures were observed, and the diamond coating obtainedwas uneven, having irregular crystallite sizes. Another variable testedin the above vapour deposition process having controlled and regulatedthermal energy transfer means, was the pressure within the depositingchamber. However, as it can be seen, variations in the pressure between6 and 15 torr had no effect on the substrate holder temperature. Thequality and morphology of the coating obtained was examined by scanningelection microscopy (SEM). It was found that a two phase compositemixture containing 20% tin and boron nitride provided the optimumconditions for obtaining uniform polycrystalline coating of even sizeddiamonds at a high deposition rate of 3 μm per hour.

EXAMPLE 2

A sintered tungsten carbide-6% cobalt containing insert of 3 mm heightand having a 10mm by 10 mm square face to be coated with diamondcoating, was placed in a single substrate holder assembly shown on FIG.3. The surface of the carbide insert was pre-treated by SiC sandblastingand ultrasonic cleaning as described in Example 1, then etched in asolution of 1:1 HCl-H₂SO₄, followed by seeding in a submicron sizeddiamond suspension in isopropyl alcohol. The pre-treated carbide insertswere individually coated utilizing different tin-boron nitride mixturesas the thermal energy transfer regulating two phase composition. Thetemperature of the substrate was measured by a thermocouple attached tothe underside the sintered carbide insert. The thermal energy transferregulating two phase BN-tin compositions included 20% and 40% tin, aswell as boron nitride without tin addition for comparison. The size ofthe boron nitride particles was less than 1 μm, and the admixed fine tinhad particle size ranging between 1 μm and 5 μm. The diamond coating wasobtained in a CVD apparatus, and under conditions similar to thatdescribed in Example 1. It was found that using boron nitride powderonly as thermal energy transfer regulating packing, resulted inirregular substrate temperatures, and no or only very poor qualitydiamond coatings could be obtained. Polycrystalline diamond coatings ofdesired quality, composed of even sized diamond crystallites of 20-30μm, were obtained with 40% tin containing BN-tin mixtures as the twophase compositions. The average rate of diamond deposition under suchconditions was 3.5 μm per hour.

EXAMPLE 3

Razor blades coated with a “diamond-like-carbon” coating were obtainedby a vapour depositing process referred to as DLC coating process. Thediamond-like-carbon coatings were produced in an apparatus utilizingfiltered cathodic arc carbon plasma, such as for example, described inU.S. Pat. No. 5,435,900, and operated at 10⁻⁵ torr pressure.

The steel blades to be coated were attached to the surface of a wellpolished, massive block of aluminum. The aluminum block was watercooled. To obtain uniform DLC coating it was essential that the thermalenergy generated by vapour deposition was transferred in a regulatedmanner by a thermally conductive compound. One face of the thin steelblades was in contact with the aluminum block by means of a thin layerof a two phase composition containing 40% gallium of particle size 45 to60 μm, in a Ga—BN mixture. The Ga—BN mixture was first suspended iniso-propyl alcohol and painted on the surface of the aluminum block toform a coating under the thin steel blades prior to applying vapourdeposition. The nano-hardness of the DLC coating obtained using thetwo-phase Ga—BN mixture as thermal energy transfer regulating medium,was measured to be 60 GPa. In comparison, vapour deposited DLC coatingson steel razor blades were obtained without the utilization of thermalenergy transfer regulating compositions of the present invention. Theresulting coatings were uneven and when tested exhibited substantiallylower nano-hardness.

The above examples describe the utilization of two phase mixtures of lowmelting metal-ceramic particles in processes for obtaining diamond ordiamond-like-carbon coatings. The thermal energy transfer regulatingmixtures may be used in other processes, chemical or physical, forobtaining vapour deposited coatings of even grain size and thickness. Itwill also be apparent that the method of regulating thermal energytransfer described herein can be applied to many other types ofprocesses for obtaining vapour deposited coating beyond the examplesgiven, for instance, coatings of ceramic materials, such as tungstencarbide, and other hard wearing ceramic materials on hard metal surfacesdeposited at elevated temperatures. The operational parameters, such asthe temperature difference between the deposition and the substratebase, composition of the two phase mixture, gas composition bearing thevapour to be deposited, vapour pressure of the depositing species etc.are adjusted according to the desired coating.

The method of regulating heat and energy transfer by utilizing a twophase mixture of high melting point ceramic particles and a low meltingpoint metal can be applied in manufacturing processes in fields otherthan vapor deposition, such as the manufacture and use of cookingutensils or pots, tube furnaces and thermal barrier shield for jets androckets as described below. It can also be utilized in such otherapplications as sintering by powder metallurgy, heat treatment and ionnitrating, for heat sink devices in electronics, thermal insulation inbuilding construction, food processing, thermal regulating in biologicalenvironments and in medical applications.

EXAMPLE 4

Cooking pots or similar utensils, made of stainless steel or othersuitable metals and having convenient size and volume can bemanufactured utilizing the heat transfer regulating mixture of thepresent invention. It is a known practice to have a stainless steel flatbottomed container equipped with a relatively high heat capacityaluminum, copper or stainless steel plate. In conventional cooking potsthe plate has a rim adapted to smoothly enclose the circumference of thecontainer and attached to the flat bottom of the container by means ofhigh temperature soldering, brazing or similar conventional methods. Therole of the aluminum, copper or stainless steel plate is to ensure evenand rapid heat transfer from an electrically heated hot plate or cookingring or a gas-burning device, in a normal cooking or household heatingoperation. One of the shortcomings of such a conventionally attachedplate to the bottom of the container is that it allows relatively rapidheat loss, in other words, the contents of the container, e.g. the foodcooked, will cool rapidly which may be undesirable.

FIG. 6 shows schematically a cooking utensil or pot 1, made ofconventional parts, that is a stainless steel container 2, having a flatbottom section 5, tightly fitting into a heavy gauge stainless steelbase cap 4, having a rim 6, adapted to enclose the container 2. A cavity3 is defined between the container 2, and rimmed base cap 4, is filledwith a composite mixture 8, according to the present invention, havingthe following composition: 40 wt % indium powder, of −325 mesh (lessthan 40 μm) size, thoroughly mixed with 60 wt % boron nitride ceramicpowder of 5 μm particle size. When placed on a gas ring or conventionalhot plate of a stove, the three component cooking pot 1, can be used asa cooking utensil in the usual manner. At the melting temperature ofindium, 156° C., the composite mixture becomes a two phase semi-solidmixture with excellent heat conducting or heat transferring propertiesensuring rapid heating of the contents of the vessel.

When a heating process using the cooking pot 1 shown on FIG. 6, isterminated, that is the contents of the cooking pot have been maintainedat the prerequisite temperature for a prerequisite period of time, theheat is turned off, resulting in the gradual cooling of the cooking potand its contents. When the temperature inside cavity 3, drops below themelting point of indium, the liquid indium solidifies, the ceramicpowder becomes dispersed in the solidified metal, leading to asubstantial slowing down in the rate of further heat transfer, that isthe cooling of the contents of the vessel. In other words, the contentsin the cooking pot can be kept warm longer.

In an other embodiment of the present invention a heater such as shownby representative heating elements 7 can be incorporated in the bottomof the cooking pot, surrounded by the thermal regulating compound 3.

EXAMPLE 5

Thermal regulating compound can be used as a thermal transfer medium fortube furnaces and related CVD reactors. A high temperature tube furnace100 is schematically shown in FIG. 7a. It consists of a tubular furnacebody 102, created by two tube liners, external liner 103 and internalliner 104. A thermal regulating compound 105 according to the presentinvention fills the space between the tubes 103 and 104. In this casethe thermal regulating compound 105 consists of 20% weight of copperpowder with particle size 3-5 μm as a component A having low meltingpoint (T_(A)˜1050° C. ) and balance fine alumina powder with particlesize 1-2 μm as a component B having a high melting point. The tubularbody 102 is surrounded by a heating array 106, made of molybdenum and anexternal thermal insulating tube 107, having an internal reflectingsurface 108. The molybdenum heaters 106 are heated by DC current,provided by a DC power supply (not shown). At a moment t_(on) when theheaters are turned on, a thermal flux q is directed on the externalsurface of the tubular body 102. When the temperature of the thermalregulating compound exceeds the melting point of copper T_(A), thecopper will melt and the thermal resistivity of the tubular body 102will drop down to the level determined by the low melting pointcomponent A. The temperature inside the furnace will increase rapidly toexceed the melting point of copper. If the heaters are turned off at amoment t_(off), the temperature of the tubular body will decreasequickly below the melting point T_(A). At that moment the copper willsolidify and the thermal resistance of both the thermal regulatingcompound 5 and the entire tubular body 2 will increase to the level,determined by the ceramic component B. From this moment the temperatureinside of the furnace will decrease very slowly due to the thermalinsulating properties of the ceramic component B of the thermalregulating compound 5 as it is diagrammatically shown in FIG. 8. It canbe seen that heat can easy propagate from the outside toward the insidespace of the furnace throughout the furnace body 2 during the heatingstage, while it keeps insulated and trapped during the cooling stagewhen the heating array 106 is turned off.

In an other embodiment, and as shown in the axial section view of FIG.7b, a heater array 153 can be incorporated in the body of a furnace 150,surrounded by a thermal regulating compound 152 for heating gas flow. Inthis case the furnace body consists of a tubular enclosure 151 filledwith a thermal regulating compound 152. A conventional ceramic thermalinsulation 154 surrounds outer surface of the furnace body 151. Bothends of the furnace are sealed by respective ceramic lids 156 and 157.The lid 157 has a discharge nozzle 159 and the lid 156 has an inlet pipe158 for injecting a gas mixture 160 respective to be heated in thefurnace 150.

EXAMPLE 6

The thermal regulating compound can be successfully used as a thermalbarrier shield against impact with high temperature atmospheric flow forsupersonic jets and space rockets. The change in concentration of lowmelting point component A allows one to regulate the thermal resistanceof the shield with a high degree of accuracy, as was shown above in FIG.5 for the CVD processing of polycrystalline diamond coatings. Anarrangement 200 for modeling thermal transfer between high temperaturesupersonic air plasma flow and a thermally resistant shield plate isschematically shown in FIG. 9. It consists of a flat shield-wall 202,having two parallel inconnel plates: a front plate 203 and a back plate204. A thermal regulating compound 205, having the same composition asin Example 5 fills the space between plates 203 and 204. A source 206 ofa supersonic high temperature jet 211 is installed in front of theshield 202. It consists of a supersonic nozzle 207, a gas inlet 208 anda resistance heater 209 connected to a DC power supply (not shown). Aback side of the shield is cooled by a forced convection means 210. Whenthe supersonic high temperature jet 211 is directed on the shield 202the temperature of the thermal compound increases and eventually reachesthe melting point of the component A. At this moment the thermalresistance of the shield drops down to allow it to protect the frontplate 3 against excessive thermal flux coming from the supersonic jet211. When the oncoming thermal flux decreases, the low melting pointcomponent solidifies and thermal resistance of the shield 202 increaseswhich keeps the temperature of the front plate 203 high providingpreferable conditions for radiation cooling.

This arrangement can be also used as a supersonic jet assisted CVDreactor as shown in FIG. 10. In this case a carbide insert 212 as asubstrate to be coated is placed near the stagnation point of hightemperature supersonic plasma flow on the front surface of the shield202. The plasma creating gas composition consists of argon (3 slm),hydrogen (0.5 slm) and methane (3 sccm). The thermal regulating compound205, contains 1-5 μm size BN powder with a 3-5 μm size 20 weight %aluminum powder composition allows the temperature on the surface of thecarbide insert 212 to be kept at 900° C. with an accuracy of+/−2%.

EXAMPLE 7

A two-phase thermal regulating compound according to the presentinvention can be used as a thermal regulating and support medium in asliding bearing arrangement to support rotating parts exposed in athermal transfer environment. FIG. 11 shows a rotating shaft 301 with aheat receiver 302 supported by a radial bearing 303, consisting of acylindrical body 304 with external cooling ribs 305 made of steel andwith two opposed graphite lids 306. The cavity created by the body 304and the lids 306 is filled with a thermal regulating compound 307 havingthe same composition as in Example 1. The shaft 301 is rotated by aconventional motor (not shown). When the temperature of the shaft 301exceeds the melting point of low melting point component of the thermalregulating compound 307 (tin) this component melts, providing anincrease in the thermal conductivity in the vicinity of the shaft 301and a simultaneous reduction in the friction between the shaft 301 andthe surrounding thermal regulating compound 307.

While the above examples have referred to specific ratios of the lowmelting point component to the particulate ceramic component, it will beappreciated that strict adherence to the specific ratios is notessential. It is expected that typically the thermal regulating compound(heat transfer regulating mixture) may have from 20 to 80% by weight ofthe metal with the balance being the ceramic component. It is furtherexpected that a more preferred range will have from 40% to 60% of themetal component.

The foregoing has described the principles, preferred embodiments andmodes of operation of the present invention. However, the inventionshould not be construed as limited to the particular embodimentsdiscussed. Instead, the above-described embodiments should be regardedas illustrative rather than restrictive, and it should be appreciatedthat variations may be made in those embodiments by workers skilled inthe art without departing from the scope of the present invention asdefined by the following claims.

I claim:
 1. A heat transfer regulating device comprising: an enclosurehaving first and second contact faces; a heat transfer regulatingmixture within said enclosure, said heat transfer regulating mixtureincluding a metallic component A having a melting point T_(A) and aparticulate ceramic component B having a melting point T_(B) above themelting point T_(A) and above a desired operating temperature T_(D),which is also above the melting point T_(A); said second component Bbeing non-reactive with and non-wettable by said metallic component A;and, said mixture having a thermal resistivity which is lower aboveT_(A) than it is below T_(A) .
 2. A heat transfer regulating device asclaimed in claim 1 wherein the metallic component A is selected from thegroup consisting of aluminum, tin, lead, gallium, indium, copper, silverand alloys thereof.
 3. A heat transfer regulating device as claimed inclaim 1 wherein said particulate ceramic component B is selected fromthe group consisting of alumina, titanium nitride, titanium carbide,titanium carbonitride, boron nitride, boron carbide, silicon carbide,silica and mixtures thereof.
 4. A heat transfer regulating device asclaimed in claim 3 wherein said particulate component B has an averageparticle size of from 1 μm to 150 μm.
 5. A heat transfer regulatingdevice as claimed in claim 3 wherein said metallic component A isselected from the group consisting of aluminum, tin, lead, gallium,indium, copper, silver and alloys thereof.
 6. A heat transfer regulatingdevice as claimed in claim 5 wherein said particulate component B has anaverage particle size of from 1 μm to 150 μm.
 7. A heat transferregulating device as claimed in claim 1 wherein said enclosure hasoppositely disposed first and second sides; said first face is on saidfirst side; and, said second face is on said second side.
 8. A heattransfer regulating device as claimed in claim 7 wherein said first andsecond sides are of metal.
 9. A heat transfer regulating device asclaimed in claim 8 wherein: said first side is a bottom inner face of acooking vessel; said first component A is indium; and, said secondcomponent B is boron nitride.
 10. A heat transfer regulating device asclaimed in claim 9 wherein: said indium is initially of less than 40 μmsized particles; said boron nitride is of substantially sub 5 μmparticle size; and, said indium and said boron nitride are present insaid heat transfer regulating mixture in a proportion of from 20% to 80%by weight iridium with the balance being boron nitride.
 11. A heattransfer regulating device as claimed in claim 9 wherein: said indium isinitially of less than 40 μm sized particles; said boron nitride is ofsubstantially sub 5 μm particle size; and, said indium and said boronnitride are present in said heat transfer regulating mixture in aproportion of from 40% to 60% by weight indium with the balance beingboron nitride.
 12. A heat transfer regulating device as claimed in claim9 wherein: said indium is initially of less than 40 μm sized particles;said boron nitride is of substantially sub 5 μm particle size; and, saidindium and said boron nitride are present in said heat transferregulating mixture in a proportion of 20% by weight indium to 80% byweight boron nitride.
 13. A heat transfer regulating device as claimedin claim 8 wherein: said first side is an external liner of a tubularfurnace body; and, said second side is an internal line of a tubularfurnace body.
 14. A heat transfer regulating device as claimed in claim13 wherein: said first component of said heat transfer regulatingmixture consists of copper; and, said second component B consists ofalumina.
 15. A heat transfer regulating device as claimed in claim 14wherein: said copper has an initial particle size of from 3 to 5 μm;said alumina has a particle size of from 1 to 2 μm; and, said copper andsaid alumina are present in a ratio of 20% by weight copper to 80% byweight alumina.
 16. A heat transfer regulating device as claimed inclaim 8 wherein: said first side is a front plate of a shield wall; and,said second side is a rear plate of a shield wall.
 17. A heat transferregulating device as claimed in claim 16 wherein: said metalliccomponent A is aluminum, initially of a 3-5 μm particle size powder;and, said particulate ceramic component B is boron nitride having aparticle size of from 1-5 μm.
 18. A heat transfer regulating deviceaccording to claim 17 wherein: said aluminum and said boron nitride arepresent in a ratio of from about 20% by weight aluminum to about 80% byweight boron nitride.
 19. A heat transfer regulating device as claimedin claim 17 wherein said aluminum and said boron nitride are present insaid heat transfer regulating mixture in a proportion of from 20% to 80%by weight aluminum.
 20. A heat transfer regulating device as claimed inclaim 17 wherein said aluminum and said boron nitride are present insaid heat transfer regulating mixture in a proportion of from 20% to 80%by weight aluminum.